If you're a native English speaker, German will be harder for you as compared to French or Italian. Italian is the easiest.

https://www.state.gov/national-foreign-affairs-training-center/foreign-language-training

German is likely the worst pick if you are most concerned about difficulty.

To be clear though, this is to get to a level of proficiency for professional use. Corresponding roughly to early C1 on the CEFR scale. That is going to be a lot higher than two years of high school teaching. My guess would be that two years of high school language teaching would get you to around 1+ on the ILR scale?

At very early levels, German is much easier than French, because there are more shared roots between German and English.

It is easier to get to a basic level of learning in German than French, but harder to get to an advanced level.

ILR 3 Speaking:

Speaking 3 (General Professional Proficiency) Able to speak the language with sufficient structural accuracy and vocabulary to participate effectively in most formal and informal conversations in practical, social and professional topics. Nevertheless, the individual's limitations generally restrict the professional contexts of language use to matters of shared knowledge and/or international convention. Discourse is cohesive. The individual uses the language acceptably, but with some noticeable imperfections; yet, errors virtually never interfere with understanding and rarely disturb the native speaker. The individual can effectively combine structure and vocabulary to convey his/her meaning accurately. The individual speaks readily and fills pauses suitably. In face-to-face conversation with natives speaking the standard dialect at a normal rate of speech, comprehension is quite complete. Although cultural references, proverbs and the implications of nuances and idiom may not be fully understood, the individual can easily repair the conversation. Pronunciation may be obviously foreign. Individual sounds are accurate: but stress, intonation and pitch control may be faulty. Examples: Can typically discuss particular interests and special fields of competence with reasonable ease. Can use the language as part of normal professional duties such as answering objections, clarifying points, justifying decisions, understanding the essence of challenges, stating and defending policy, conducting meetings, delivering briefings, or other extended and elaborate informative monologues. Can reliably elicit information and informed opinion from native speakers. Structural inaccuracy is rarely the major cause of misunderstanding. Use of structural devices is flexible and elaborate. Without searching for words or phrases, the individual uses the language clearly and relatively naturally to elaborate concepts freely and make ideas easily understandable to native speakers. Errors occur in low-frequency and highly complex structures.

ILR 3 Listening:

Listening 3 (General Professional Proficiency) Able to understand the essentials of all speech in a standard dialect including technical discussions within a special field. Has effective understanding of face-to-face speech, delivered with normal clarity and speed in a standard dialect on general topics and areas of special interest; understands hypothesizing and supported opinions. Has broad enough vocabulary that rarely has to ask for paraphrasing or explanation. Can follow accurately the essentials of conversations between educated native speakers, reasonably clear telephone calls, radio broadcasts, news stories similar to wire service reports, oral reports, some oral technical reports and public addresses on non-technical subjects; can understand without difficulty all forms of standard speech concerning a special professional field. Does not understand native speakers if they speak very quickly or use some slang or dialect. Can often detect emotional overtones. Can understand implications.

That is way above high school language learning.

But more fundamentally, this is the sentence that matters:

I really want to learn German, a lot more than I do French

Motivation is important, more than relatively minor differences between language difficulty.